I am not aware of any guarantee for this, as it is a voluntary process. But others may have suggestions.

Thanks for the quick response. So you are saying there is no way available to the sender to query the network of service providers to find out which was the last service node that acknowledged with a handshake that the message was received.

This article may be helpful:

  http://kb.mozillazine.org/Figuring_out_whether_the_recipient_read_your_message

Well, I did request both the Return receipt and Delivery status notification. From the http://kb.mozillazine.org/Figuring_out_whether_the_recipient_read_your_message webpage my understanding is that I get a DSN response if and when the recipient's server got the message. Since I have not received anything back, looks like this means that either the recipient's server has not received the message or the server implemented a way to block the return receipt. Thank you for your help, I will need to call the company...

The reality is that in most cases you will get nothing.

DNS responses have largely been disabled on almost all mail servers. They clearly still exist in some quarters, as we still get the occasional complains about being notified of undelivered messages that were not sent.

The underlying cause of this disabling is what is known as backscatter. Unfortunately mail servers were being blacklisted for spam because they would be sending thousands of these non delivery notices. The simple solution is to turn that feature off on your mail server.

Then there are the read receipts. These can and sometimes are disabled at th3 server level, even in Thunderbird's default configuration they are set to ask, the really it is an exception rather than a rule that folk allow one to be sent. I sort of base this on the complaints we see here for folk that are not happy that their exchange server is making the decisions for them as Microsoft sets the default on that system to automatic and does not allow the user a choice at all.

Something folk in general are not aware of, largely because of the general overall reliability of email, is that there is nothing in any of the specifications or standards about reliability of delivery or for that matter an attempt to deliver even being made. There is certainly nothing like the old paper based signature at delivery that can be fed back to the sender that has the legal authority to assure delivery.